Valve element opening/closing devices have been conventionally known in which a valve element is driven by a motor as a drive source to open and close a flow passage for refrigerant in a refrigerator or the like. In Japanese Patent Laid-Open No. 2002-349740, a valve element opening/closing device is disclosed in which a valve element is mounted on a screw member and the valve element is advanced or retreated in its axial direction by means of that the screw member is rotated by a motor to cause a flow passage into which refrigerant flows to open and close. In the valve element opening/closing device, a mechanical structure such as the number of input/output ports and its control method are determined depending on its application and disposed location.
For example, in Japanese Patent Laid-Open No. 2001-241825, a structure of a refrigerator-freezer is disclosed in which a defrosting valve is disposed at an upstream side position of an evaporator for freezing compartment for controlling temperature and defrosting in the freezing compartment (see FIG. 10 etc.). The defrosting valve is a valve in which one of three kinds of refrigerants with different temperatures to be inputted is selected and controlled to flow into the evaporator for freezing compartment and which is provided with a plurality of input ports (three input ports and one output port).
However, in the valve element opening/closing device shown in the former Patent Reference, when a flow passage for fluid is to be closed, the valve element is required to operate against a pressure of fluid which flows into the device. Therefore, in order to securely close the flow passage, a measure may be required, for example, a newly reduction gear is required to be added or a torque of the motor is required to increase. As a result, a size and a manufacturing cost of the valve element opening/closing device are increased.
Further, as described in the latter Patent Reference, in the valve element opening/closing device in which a plurality of inputted fluids is selectively controlled to flow out, a total sum of fluid pressures inputted into the device may be larger. Therefore, a force for closing the flow passage for fluid is required to farther increase and thus the size of the valve element opening/closing device and its manufacturing cost are further increased.